The present invention relates to a control method and apparatus for an air conditioner, and more particularly to a control method and apparatus suitable for an automobile air conditioner wherein the quantity and temperature of air flow are controlled in accordance with various changes of ambient temperature outside the passenger compartment of an automobile.
As shown in FIG. 1, a conventional control system for an air conditioner comprises a set circuit 1 for producing an output signal indicative of a desired temperature T.sub.set of air in a compartment to be conditioned, a temperature sensor 2 for producing an output signal indicative of the actual temperature T.sub.r of air in the compartment, and a detector 3 responsive to the output signals from set circuit 1 and sensor 2 for detecting any deviation between the desired temperature T.sub.set and the actual temperature T.sub.r and for producing an output signal indicative of the detected deviation. A temperature controller 4 receives the output signal from detector 3 to control the temperature of air flow in accordance with the deviation so as to adjust the actual temperature T.sub.r to the desired temperature T.sub.set and maintain it at the same.
During operation of temperature controller 4, the sensor 2 acts to produce a feedback signal indicative of any change of the actual temperature in the compartment, and the controller 4 acts to adjust the actual temperature T.sub.r to the desired temperature T.sub.set in response to the feedback signal from sensor 2. In this instance, the heat load in the compartment fluctuates in accordance with variations of the outside ambient temperature T.sub.am, and subsequently the actual temperature T.sub.r fluctuates due to delay of heat transfer in the compartment. To restrain fluctuation in the actual temperature in the compartment, an outside ambient temperature sensor 6 and an adder 7 are provided to preliminarily compensate the fluctuation of heat load caused by a change of the outside ambient temperature T.sub.am. Furthermore, the sensor 2 is arranged to compensate the fluctuation of heat load caused by sunshine entering the compartment.
In the control system described above, assuming that the quantity of air flow is at a constant value, the temperature of air flow is adjusted by controller 4 as represented by the following equation. EQU T.sub.ao =K.sub.set .multidot.T.sub.set -K.sub.am .multidot.T.sub.am -K.sub.r .multidot.T.sub.r +C
where T.sub.set is the desired temperature in the compartment, T.sub.am is the outside ambient temperature, T.sub.r is the actual temperature in the compartment, C is a constant, and K.sub.set, K.sub.am and K.sub.r are respective gains of set circuit 1, and sensors 6 and 2. This means that the quantity of air flow is considered as a constant factor, and that only the temperature of air flow is adjusted by temperature controller 4 to adjust the actual temperature T.sub.r toward the desired temperature T.sub.set.
In another conventional control system for the air conditioner, the quantity of air flow is controlled either in accordance with variation of the temperature of air flow or the deviation between the actual temperature and the desired temperature. In this instance, however, the temperature of air flow is calculated on the basis of the quantity of air flow normally required in use.
In controlling the air conditioner, it is desirable that the quantity and temperature of air flow are controlled in accordance with such changes of surroundings as intensity of sunshine, change of the seasons, and the like. It is also desirable that in summer, the quantity of air flow is increased to enhance the feeling of draft in the compartment and is decreased in winter to enhance the feeling of warmth due to the high temperature of air flow, and that the quantity of air flow is increased in accordance with the intensity of sunshine to enhance the feeling of draft without any fluctuation of the actual temperature in the compartment. However, these requirements may not be fulfilled in the conventional control systems described above.